This invention is related to apparatus and processes for separating gases from solids. More particularly, it is an apparatus and a process for separating the flue gas from regenerated catalysts used in catalytic conversion processes of petroleum hydrocarbons.
Catalytic pyrolysis is a process for producing light olefins such as ethylene, propylene, as major desired products from heavy petroleum hydrocarbon feedstocks. The major procedure of this process is: heavy petroleum hydrocarbon feedstocks come into contact with a solid acid catalyst under conditions of a reaction temperature of 650-750xc2x0 C., a reaction pressure of 0.15-0.4 MPa, a reaction time of 0.2-5 s, a catalyst to feed oil weight ratio (abbreviated as catalyst/oil ratio below) of 15-40:1, a steam to feed oil weight ratio of 0.3-1:1, and in the presence of high temperature steam to conduct catalytic pyrolysis process in a riser or downer reactor. The reaction products, steam and the coked catalyst are separated through a rapid gas-solid separation procedure and obtained major desired products are ethylene and propylene; the coked catalyst enters the regenerator after steam stripping and comes into contact with oxygen-containing gas to conduct coke burning for regeneration, and the hot regenerated catalyst returns to the reactor for recycle use.
Because there are a great number of pores in the catalyst, the flue gas remains in the pores and on the surface of the catalyst. Although the amount of the flue gas remaining in each pore is small, quite a deal of flue gas is carried into the reactor by the regenerated catalyst owing to the great catalyst/oil ratio and the great amount of the recycled catalyst. For a catalytic pyrolysis process unit with capacity of 1 million tons per year, if the recycle ratio is 0.4 and the catalyst/oil ratio is 20, the amount of the recycled catalyst is 3500 t/h and the amount of the flue gas carried into the reactor is about 3500 m3/h, making up more than 10% of the dry gas. The flue gas contains N2, O2, CO2, CO, NOx, SOx etc. If the regenerated catalyst is directly fluidized and fed into the reactor, the flue gas is entrained by the regenerated catalyst into the reactor and becomes impurity gas, which not only increases the load of the compressor, but also hinders the normal operation of the subsequent cryogenic separation. Therefore, it is a vital problem for catalytic pyrolysis process to remove the flue gas from the regenerated catalyst. For other catalytic conversion processes, the problem of much flue gas entering the reactor is also present when the catalyst/oil ratio is rather great.
U.S. Pat. No. 4,051,013 teaches the use of a regenerated catalyst stripper in which the flue gas adsorbed on the catalyst and among the particles is stripped away through bringing the stripping medium (generally it is steam) into countercurrent contact with the regenerated catalyst. The stripping gas is introduced into the stripper from bottom and the stripper contains baffles, but this patent does not describe the particular shape and structure of the baffle. This patent is practically unusable because it ignores the problem of deactivation of the catalyst at high temperature by the hydrothermal action of the steam.
CN 1154400A proposes that the regenerated catalyst is treated using a temperature-adjusting degassing drum and that the fluidizing and stripping medium is dry gas. The major component in the temperature-adjusting degassing drum is a vertical heat-removing pipe because the major objective is to change the temperature of the catalyst entering the reactor. It is impossible to control the growth of the bubbles by this structure, resulting in the worsening of the gas-solid contact and a poor stripping efficiency. Moreover, the competitively adsorbing ability of the dry gas is weak and the replacing efficiency is low. Therefore, more dry gas must be consumed to attain the same content of the flue gas contained in the regenerated catalyst after stripping. Besides, the dry gas is mixed with the flue gas during the operation, so it can not further be used and the profit is poor.
During catalytic pyrolysis process, the temperature of the regenerated catalyst is in the range 700-750xc2x0 C. and if it contacts with the steam for a long time, it will deactivate. Therefore, the stripping process for the regenerated catalyst proposed in U.S. Pat. No. 4,051,013 is not suitable to the treatment of the regenerated catalyst in catalytic pyrolysis process for removing the flue gas. The process and the structure of the device proposed in CN 1154400A also have some shortcomings.
One object of the present invention is to provide a regenerated catalyst stripper.
Another object of the present invention is to provide a process for stripping the flue gas from regenerated catalysts.
The stripper provided in the present invention is characterized in that it is a vertical cylinder and comprises:
(1) a degassing pipe located at longitudinal axis;
(2) a horizontal pipe connected with the lower end of the degassing pipe,
(3) several sets of inner annular baffles fixed on the degassing pipe, the degassing pipe having holes below each set of the inner annular baffles;
(4) several sets of outer annular baffles fixed on the inner wall of the cylinder, the outer annular baffles having some small holes,
the inner annular baffles and the outer annular baffles being arranged along the vertical direction in alternative arrangement and with some spacing;
(5) annular steam conduits with some small holes located in the spaces below each set of the outer annular baffles;
(6) steam introducing conduits connected with the annular steam conduits;
(7) a gas outlet at the top of the cylinder;
(8) a catalyst inlet at the upper part of the cylinder; and
(9) an outlet of the stripped catalyst at the bottom of the cylinder.
The stripping process for removing the flue gas carried by the regenerated catalyst provided in the present invention is as follows:
the process comprises:
(1) providing the stripper aforesaid;
(2) passing the regenerated catalyst into the stripper from its upper part,
the catalyst flowing downwards via gravity, each set of the inner annular baffles directing the catalyst to flow outwards towards the same set of the outer annular baffles and then the set of the outer annular baffles directing the catalyst to flow towards the next set of the inner annular baffles, thereby several sets of the inner annular baffles and the outer annular baffles at different heights cause a zigzag flow of the catalyst in the cylinder;
(3) introducing a steam to the annular steam conduits through the steam introducing conduits,
the steam flowing out from the small holes on the annular steam conduits passing through the small holes in the outer annular baffles and coming into a countercurrent and crosscurrent contact with the regenerated catalyst,
the steam rapidly replacing the flue gas carried by the regenerated catalyst, the removed gas and the excessive steam being collected under each set of inner annular baffles and entering the degassing pipe through the opening part of the degassing pipe;
(4) discharging the regenerates catalyst from the bottom of the stripper and;
(5) venting the removed flue gas and excessive steam in the degassing pipe from the top of the stripper under the action of steam or air from the horizontal pipe.
The stripper and the strapping process for removing the flue gas carried by lie regenerated catalyst provided in the present invention are used in deep catalytic cracking or catalytic pyrolysis process with a rather high catalyst/oil ratio, but also is used in the conventional catalytic cracking or other improved catalytic conversion processes.